Field of the Invention
The invention concerns an apparatus for detecting vital functions of living bodies, and more particularly to an apparatus for detecting vital functions of living bodies by means of electromagnetic signals.
The inventors found that living bodies and therefore also human living bodies surprisingly influence high-frequency electromagnetic signals by virtue of their most important vital functions, that is to say their heartbeat and their respiration activity.
Those vital functions generally take place within known frequency ranges, which with the human heart rate can be from about 0.5 through 3.4 Hz and normally are about 1 through 2 Hz and in the case of respiration can extend between 0.1 and 1.5 Hz. That defines characteristic frequency ranges. Upon the reception and recording of electromagnetic signals those frequency ranges are visible when people are in the reception region. In addition it is possible to provide information about the number of people located, on the basis of received and also processed signals. In that respect, use is made of the principle of biological variety and specificity, on the basis of which the heart and respiration frequency patterns of different people differ. For four or more people however, it is generally no longer possible clearly to distinguish between the number of people by virtue of the frequency superimposition of the respective frequencies. As from that number of people it is then only possible to provide the information that: there are at least four people present.
In any event a frequency range of 0.01 through 10 Hz includes all frequencies which are of interest in terms of the vital functions of a human body.
What was surprising was the realisation that even without emitted transmission power, just the receiver device together with the device for obtaining the frequency components which are characteristic of living bodies the inventors were in a position to provide the desired identification effect for the vital functions.
This means that the presence of a living body, at least in the vicinity of the receiver device, already results in detectable signal components in the specified frequency ranges, without in that respect the need for through-radiation with a carrier signal.
With the receiver device for electromagnetic signals and the device for obtaining frequency components which are characteristic in respect of living bodies, without additional emitted signals, the inventors were already in a position of reliably detecting living bodies at up to more than 3 meters distance or approximately the distance of the storey of a building.
In the simplest embodiment of the invention the direct demodulator described hereinafter, in the form of a diode direct receiver for receiving the frequency components which are characteristic in respect of living bodies, was already sufficient.
In addition transmitters were later used, with which through-radiation of the detection area was effected, and reflected, transmitted or scattered radiation was received, the investigation thereof for pronounced frequency components providing the proof of the presence of living bodies.
So that electromagnetic radiation can still be received through dense debris, even at some distance, frequencies of the electromagnetic radiation of some hundred megahertz to about 10 gigahertz were used, which ensured a high depth of penetration.
That radiation experienced phase modulation which added side bands displaced by some Hertz to the high-frequency carrier signal. With conventional reception procedures, detection of frequency bands which are so close together would have required short term-stable oscillators with deviations of less than 10.sup.-12, which hitherto was considered to be unattainable at reasonable cost. That problem is made more acute by the low levels of received signal powers.
Some of the advantages of the embodiments described herein are discussed hereinafter.
The use of known phase modulators initially appears obvious. Homodyne, heterodyne and PLL (Phase Locked Loop) methods and the excitation of the flanks of a local oscillation circuit are known. It has been found however that none of the foregoing processes was capable of supplying the desired results at an expenditure that was reasonable. It was only the use of a direct demodulator which permits direct separation of the modulation frequency from the modulated frequency, that leads to the desired results. It is assumed however that, with suitable apparatus expenditure and improved circuit arrangements, the foregoing methods can be used in accordance with the present invention.
With a component with a non-linear current/voltage characteristic as the frequency-selective element, it was possible to provide inexpensively and reliably for demodulation of the frequency components which are of interest. A diode, a bipolar or a field effect transistor could be successfully used as the element with a non-linear characteristic.
Those components are both inexpensively obtainable and also non-critical in regard to their use. The optimum working range of those components of from about 100 kHz to 200 MHz could be used at higher reception frequencies by means of a frequency conversion device connected upstream of the demodulator. Although that frequency conversion device added tolerable distortion in the time region to the signal, it did however superimpose only a slight amount of additional noise.
The signal to be received could be raised with a transmitter device for transmitting an electromagnetic carrier signal at a fixed frequency; however a very high level of attention had to be paid to the stability of the carrier frequency in order to exclude undesirable modulation effects in the frequency range which is of interest. A simple quartz-stabilised analog transmission circuit with an oscillator circuit of high quality surprisingly showed itself to be a suitable oscillator, after an adequate transient or build-up time.
The method and the apparatus according to the invention can also be used for object monitoring and/or safeguarding. The specific embodiments show, at a later point in this description, static monitoring arrangements.
The use of an analog sampling filter, unlike high-frequency digital filters, did not exhibit any detrimental additional frequency components and crucially contributed to the quality of the signal obtained. Additional undesirable signal components such as for example noise and superimposed interference were prevented by limiting the band width of the electromagnetic signal prior to the sampling operation and prior to A/D-conversion to high frequencies.
The use of an analog high pass filter for preventing low-frequency components in respect of the frequency-dependent 1/f-noise of the transmission oscillator and internal structural units was also important.
The unexpectedly good operation of the apparatus according to the invention and the method according to the invention also permits use thereof in many areas.
People who are in danger of committing suicide can be monitored in psychiatry or in places of detention, without requiring constant inspection by personnel who are in charge of such people.